MAE SOT, Thailand (Reuters) - A leader of Myanmar's biggest rebel group was shot dead at his home in a Thai border town on Thursday in an assassination immediately blamed on troops loyal to the former Burma's military junta.

Mahn Sha Lar Phan, secretary-general of the Karen National Union (KNU), was shot at his two-storey wooden home by two men who arrived in a pickup truck, his wife Kim Suay told Reuters at the scene. He died instantly.

"One of them walked up to the house and said in Karen 'How are you, uncle?' Then the other man joined him after parking the truck and they both shot him with two pistols," she said, her voice shaking with emotion.

In an interview with Reuters on Monday, he had predicted a possible increase in violence ahead of a constitutional referendum in the former Burma in May.

However, the KNU and its armed wing, the Karen National Liberation Army (KNLA), are riven by internal feuds and lethal vendettas.

His son Hse Hse, another senior member of the predominantly Christian Karen rebel movement, blamed a Buddhist Karen splinter group which brokered a truce with the Myanmar junta in the mid-1990s.

"This is the work of the DKBA and the Burmese soldiers," Hse Hse said, refering to the Democratic Karen Buddhist Army.

The Karen have been fighting for independence in the hills of eastern Myanmar for the last 60 years, one of the world's longest-running insurgencies.

Thai police said they had the registration number of the truck and were setting up roadblocks around Mae Sot, a "wild west" frontier town of refugees, illegal migrants and gem dealers, to try to catch the two killers.

(Reporting by Somjit Rungjumratrussamee; Writing by Nopporn Wong-Anan; Editing by Ed Cropley and Sanjeev Miglani)

Karen National Union (KNU) soldiers attend a parade to mark the 59th anniversary of Karen Revolution Day at Thay Bay Hla in the Karen State along the Thai-Myanmar border January 31, 2008. REUTERS/Chaiwat Subprasom

The leader of the Karen National Union, one of the biggest ethnic groups fighting Myanmar's military government, was killed Thursday in Thailand, police said.

KNU General Secretary Mahn Sha was shot at his home in Mae Sot by three men who arrived in a pickup truck, Thai police Col. Pasawat Tangjui said.

He said the killing may have been the result of internal differences in the rebel group.
The KNU is one of more than a dozen ethnic groups that for decades have sought greater autonomy from Myanmar's central government. Many other groups have signed formal cease-fires with the ruling junta since 1988, but the Karen never reached a formal agreement to lay down their arms.

The group once had a powerful guerrilla army in Myanmar's eastern border region, but Myanmar army offensives, coupled with divisions within the organization, have reduced the guerrilla group's military presence considerably over the past decade.

Most of the group's senior leadership resides inside Thailand, while its military bases are mostly located just across the border in Myanmar.

Mahn Sha was sitting on a balcony on the second floor of his house when the three men arrived in the truck, Pasawat said by telephone from Mae Sot.

"One guy went upstairs, greeted Mahn Sha and then shot him at close range. Then, another guy came up and shot him again before they fled in the same vehicle," he said. The driver remained in the truck, Pasawat said.

"Initial investigations showed that the assailants are also Karen, and after speaking to some witnesses, we believe it was an internal problem within the KNU that prompted the assassination. Still, we have to investigate further to know for sure," he said.

Mahn Sha, 64, took over leadership of the KNU in 2000 from his ailing predecessor, Bo Mya, who died in 2006. He had been with the KNU since 1963, becoming Bo Mya's personal assistant and joint general secretary in 1995 before taking the top post.

In Beijing, meanwhile, China said it would support the efforts of U.N. envoy Ibrahim Gambari to help bring reconciliation to Myanmar.

"China is going to support the mediation efforts of Gambari and the secretary general of the United Nations," Foreign Ministry Spokesman Liu Jianchao said at a news conference Thursday.

Gambari's visit to China, which does considerable trade with Myanmar, comes after Myanmar's main opposition party staged a street protest this week to complain that the ruling junta's recent moves toward democracy were not enough.

Gambari is scheduled to visit Beijing on Monday and Tuesday, before flying to Jakarta and Singapore.

Copyright © 2008 The Associated Press

Story Highlights

• Karen National Union secretary-general was shot and killed
• Ethnic rebel group calls death assassination by the Myanmar junta
• Man Sha killed in attack at home by two gunmen

BANGKOK, Thailand (CNN) -- The Karen National Union secretary-general was shot and killed Thursday in what the ethnic rebel group is calling an assassination by the Myanmar junta, a KNU official told CNN.

Myanmar's junta blames the KNU for waging attacks to destabilize the military.

Two gunmen attacked Man Sha at his home in Mae Sot, a town on the Myanmar-Thailand border, the official said.

He described Man Sha as one of the most important people in the rebel group, which he said has received numerous warnings that Myanmar's military leaders planned to target and kill KNU leaders.

KNU is a major rebel group that operates in the border area that is trying to establish autonomy for the Karen ethnic minority.

The government of Myanmar, also known as Burma, blames the KNU for waging attacks to destabilize the military junta that has run the country for two decades.